LONDON, England -- UK Prime Minister Tony Blair has forecast more violence in Iraq ahead of planned January elections but says he has not yet decided on a U.S. request for back-up from UK troops.

Amid a heated Question's Time session in the House of Commons Wednesday, Blair denied accusations that the request was being driven by American politics.

The most likely candidate for the role is thought to be the elite Black Watch, which is currently the reserve battalion in the British-controlled southern sector of Iraq, which has been relatively peaceful.

Blair said it was a military decision and would be considered on an operational, not a political, basis. If the Black Watch regiment was asked to stay it would be home before Christmas, he said.

The PM warned: "We are about to enter a period of increased activity in Iraq. This has nothing to do with the the American elections. It has everything, however, to do with the Iraqi elections in January."

The prospect of British soldiers serving in more dangerous parts of Iraq has horrified many politicians, who are demanding a vote, something ministers have ruled out.

Opposition Conservative leader Michael Howard said he would not push for a parliamentary vote, effectively ruling such a move out.

CNN's European Political Correspondent Robin Oakley says however that Blair appeared to have reached a "tipping point" with lawmakers in his own party, many of whom were saying "enough is enough."

"There is a huge suspicion in the Labour Party that there is a political motivation behind this," Oakley said.

The key question, he said, was put by Howard -- why with 130,000 U.S. troops in Iraq why was it so necessary and so important to move 600 British troops up to another sector?

One military chief, Oakley added, had talked of "the Tony wants syndrome."

This theory, said Oakley, held that Blair had decided to help U.S. President George W. Bush and now required the military, the civil service and his own Labour MPs to fall into line to back him "to find the reasons he wants for the action in the first place."

Liberal Democrat leader Charles Kennedy told parliament his party would oppose any deployment which did not come at the request of British commanders on the ground.

With the presidential election less than two weeks away, MPs fear Bush wants to use a British redeployment to refute opponent John Kerry's claim that U.S. isolation has left American troops carrying the can in Iraq.

Blair insisted Tuesday night the request had come from the U.S. military, not the White House.

"This has been a request by the American military to the British military, not a request politically from the U.S. president to me," he said.

"No decision will be taken to redeploy British troops unless it is clear militarily that that should and can happen."

The Americans want the British to "back fill" for them, freeing up U.S. troops to join the intensifying assault on the insurgent stronghold of Falluja.

But Labour lawmaker Andrew Mackinlay said he and most of his colleagues did not believe that the U.S. could not fill the troop gap with its own forces.

"We have to say thus far and no further," he argued. "We have given 110 percent, and I think they are just asking too much of us."

MPs were likely to be further angered by a report in The Daily Telegraph on Wednesday that despite Blair's denials, the troop decision was made more than a week ago.

"It was decided and virtually under way," the newspaper quoted a defense source as saying, describing as "nonsense" government claims that no decision had been taken.

The Ministry of Defence said the report was "wrong and misleading."

Blair's government has not confirmed officially where the Americans want British troops to deploy.

Reports have suggested that U.S. commanders have asked the British to fill in for them in Iskandariya, 25 miles south of Baghdad, releasing the 24th Marine Expeditionary Force for other operations.